Overview of Java Language

Difference between Java and C++

Java is a true object-oriented language while C++ is basically C with object-oriented extension. Java appears to be similar to C++ when we consider only the “extension” part of C++. However, some object-oriented features of C++ make the C++ code extremely difficult to follow and maintain.

Listed below are some major C++ factures that were intentionally omitted from java or significantly modified.

• Java does not support operator overloading.
• Java does not have template classes in C++.
• Java does not support multiple inheritance of classes. This is accomplished using a new feature called “interface”.
• Java does not support global variables. Every variable and method is declared within a class and forms part of that class.
• Java does not use pointers.
• Java has replaced the destructor function with a finalize() function.
• There are no header files in java.

JAVA AND INTERNET:

Java is strongly associated with the internet because of the fact that the first application program written in java was Hot Java, a web browser to run applets on internet. Internet users can use java to create applet programs and run then locally using a “Java- enabled browser” such as Hot Java. They can also use a java-enabled browser to download and applet located on a computer anywhere in the internet and run it on this local computer. In fact, java applets have made the internet a true extension of the storage system of the local computer.

Internet users can also set up their web sites containing java applets that could be used by other remote users of internet. The ability of java applets to hitch a ride on the information super highway has made java a unique programming language for the internet. In fact, due to this, java is popularly known as internet language.

JAVA AND WORLD WIDE WEB:

World Wide Web (WWW) is an open-ended information retrieval system designed to be used in the internet’s distributed environment. This system contains what are known as web pages that provide both information and controls. Unlike a menu-driven system where we are guided through a particular direction using a decision tree structure, the web system is open-ended and we can navigate to a new document in any direction as shown. This is made possible with the help of a language called hypertext markup language (HTML). Web pages contain HTML tags that enable us to find, retrieve, manipulate and display documents worldwide.

Java was meant to be used in distributed environments such as internet. Since, both the web and java share the same philosophy, java could be easily incorporated into the web system before java, the World Wide Web was limited to the display of still images and texts. However, the incorporation of java into web pages has made it capable of supporting animation, graphics, games and a wide range of special effects. With the support of java, the web has become more interactive and dynamic. On the other hand, with the support of web, we can run a java program on someone else’s computer across the internet.

Java communicates with a webpage through a special tag called <APPLET>.

JAVA SUPPORT SYSTEMS:

It is clear from the discussion we had up to now that the operation java and java- enabled browsers on the internet requires a variety of support systems. Lists the systems necessary to support java for delivering information on the internet.

Java Environment:

The developments tools are part of the system known as Java Development Kit(JDK) and the classes and methods are part of the Java Standard Library(JSL), also known as the Application Programming Interface(API).

JDK Contains:

1. applet viewer : Enables us to run Java
2. java : Java Interpreter (By reading byte code files)
3. javac : Java Compiler, convert Java source code to byte code
4. javadoc : Creates HTML format document.
5. javah : Produces Java header files for use with native
6. javap : Java dis assembler, which enables us to convert byte code files in to a program description.
7. jdb : Java debugger, which helps us to find errors in our

API Contains:

1. Language support package: Collection of classes and
2. Utility package: Provide utility functions such as date and time
3. Input Output package
4. Networking package
5. AWT(Abstract Window Toolkit) package
6. Applet package

JVM (Java Virtual Machine):

• Java is platform independent language because the Java compiler compiles the code to byte code that is underst and by the Java environment.
• The Java compiler compiles the code to bytecode that is understand by the Java
• The bytecode is the result of compiling a Java program. You can execute this code on any platform. Due to the byte code compilation process and interpretation by a browser, Java programs can be executed on a variety of hardware and operating
• The Java interpreter can execute Java code directly on any machine on which a Java interpreter has been installed.

            Java code is portable. There fore, other people can use the programs that you write in Java even if they have different machines with different operating systems.

API (Application Programming Interface)

General Structure of a Java Program

• Documentation Section
• Package Statement
• Import Statement
• Interface Statement & Definition
• Class Definition
• Main Method Class Definition